Calcium, Bone & Mineral Metabolism

Parathyroid Hormone (PTH) Physiology

•    ↑ Serum Ca²⁺ via:

o    Bone resorption

o    Renal calcium reabsorption

o    Activates vitamin D → ↑ gut calcium absorption

•    Also causes phosphate excretion

Primary Hyperparathyroidism

•    Autonomous PTH secretion (usually parathyroid adenoma)

•    Features: "stones, bones, groans, and psychiatric overtones"

o    Renal stones, bone pain, abdominal symptoms, depression, confusion

•    Labs: ↑ Ca²⁺, ↑ PTH, ↓ phosphate, ↑ ALP

•    Imaging: Sestamibi scan or neck ultrasound

•    Treatment: parathyroidectomy if symptomatic or meeting criteria (age <50, renal/bone involvement)

Secondary Hyperparathyroidism

•    Low calcium → compensatory ↑ PTH

•    Causes:

o    Chronic kidney disease (↓ vitamin D activation, phosphate retention)

o    Vitamin D deficiency

•    Labs: ↓ Ca²⁺, ↑ PTH, ↑/normal phosphate, ↑ ALP

•    Treatment: correct underlying cause (e.g. vit D supplementation, phosphate binders in CKD)

Hypocalcaemia

•    Features: tetany, perioral tingling, seizures, Chvostek’s & Trousseau’s signs, prolonged QT

•    Causes:

o    Post-surgical hypoparathyroidism

o    Hypomagnesaemia (impairs PTH secretion)

o    Vitamin D deficiency

o    CKD

•    Labs: ↓ Ca²⁺, consider Mg²⁺, PTH, vitamin D levels

•    Treatment: IV calcium gluconate (acute), oral calcium/vit D (chronic)

Osteomalacia / Rickets

•    Vitamin D deficiency → defective bone mineralisation

•    Causes: malabsorption, CKD, anticonvulsants, poor sunlight/diet

•    Features: bone pain, muscle weakness, fractures, waddling gait

•    Labs: ↓ Ca²⁺, ↓ phosphate, ↑ ALP, ↓ 25(OH) vitamin D

•    Treatment: vitamin D and calcium replacement

Osteoporosis

•    Reduced bone mass with normal mineralisation

•    Risk factors: age, menopause, steroids, smoking, alcohol, immobility

•    Common sites: spine, hip, wrist

•    Diagnosis: DEXA scan – T-score < –2.5

•    Labs: normal Ca²⁺, phosphate, ALP

•    Treatment:

o    Bisphosphonates (alendronate – osteonecrosis of jaw risk)

o    Calcium + vitamin D

o    Lifestyle: weight-bearing exercise, smoking cessation

o    Consider: denosumab, HRT, teriparatide (in severe cases)

Paget’s Disease of Bone

•    Focal disordered bone remodelling: ↑ osteoclast and osteoblast activity

•    Features: bone pain, deformity, hearing loss (skull involvement), high-output cardiac failure (rare)

•    Labs: ↑ ALP, normal Ca²⁺ and phosphate

•    Imaging: X-ray – cortical thickening, lytic/sclerotic areas

•    Treatment: bisphosphonates (e.g. zoledronate), analgesia